It is known that hadron therapy is the modern cancer teletherapy that uses beams either of protons or of heavier nuclear charged particles with mass number larger than 1.
It is equally known that in protontherapy, which is a particular hadron therapy technique based on the use of proton beams, therapeutic beams of relatively low current (of the order of some nanoamperes) are used, with energies in the range 60 to 250 MeV.
It is also known that, in the case of different ion species, therapeutic beams with lower currents and higher energies are required compared to the ones for the protons. For example, in the case of carbon ions 12C6+, the required energies are between 1.500 and 5.000 MeV (i.e. 120 and 450 MeV/u) and currents of a fraction of nanoampere.
In this field of teletherapy different types of accelerators are used: cyclotrons (isochronous or synchrocyclotrons; conventional or superconducting) or synchrotrons.
Recently Fixed Field Alternating Gradient (FFAG) accelerators have also been considered.
Linear accelerators (linacs) have been proposed by the Requestor for both proton and light ion therapy. 1) U.S. Pat. No. 6,888,326 B2 “Linac for Ion Beam Acceleration, U. Amaldi, M. Crescenti, R. Zennaro. 2) U.S. patent application Ser. No. 11/232,929 “Ion Accelerator System for Hadrontherapy, Inventors: U. Amaldi, M. Crescenti, R. Zennaro, filed on 23, Sep. 2005. 3) “Proton Accelerator Complex for Radio-isotopes and Therapy, U. Amaldi, filed on 24. Apr. 2006.
Several companies offer turn-key centres for proton and/or carbon ion therapy. Typically a centre for more than 400-500 patients/year is located in a large multi-floor building, specially made to host the high-tech apparata, offices and services for the personnel and the reception of the patients for a total surface of many thousands square metres. It features a hadron accelerator (cyclotron, synchrocyclotron, synchrotron, linac or a combination of these) and a system of magnetic beam transport channels to irradiate solid tumours with 2-4 gantries, which rotate around the patient, and one or more horizontal therapeutic beams. A complete multi-room centre with its infrastructures requires an investment that is in the range 60-130 million Euro, the larger figure corresponding to a ‘dual’ carbon ion and proton multi-room facility.
Hadron therapy has a large potentiality of further developments, as indicated by the epidemiological studies performed in Austria, France, Italy and Germany, that have been reported, for example, in “Carbon ion therapy, Proceedings of the HPCBM and ENLIGHT meetings held in Baden (September 2002) and in Lyon (October 2003)” [Radiotherapy and Oncology 73/2 (2004) 1-217]. However these potentialities are hindered by the necessity of large capital investments to construct multi-room facilities. The potentialities can be summarized by recalling that the quoted studies reach the conclusion that in the medium-long term about 12% (3%) of the patients treated today with ‘conventional’ radiotherapy (i.e. with high-energy photons) would be better cured and/or have less secondary effects if they could be irradiated with proton (carbon ion) beams.
Only 1-2% of the 12% tumour indications for proton therapy are accepted by most radiation oncologists. The other 10% of the patients is not considered today as carrying elective indications for proton therapy by many specialists. This in spite of the fact that they would certainly profit from this irradiation modality, since the tumours are close to critical organs and it is proven that a 10% increase in the dose—for the same irradiation of critical organs—implies a 15-20% increase of the Tumour Control Probability (TCP). However it is sure that, with the accumulation of clinical trials, the first fraction of the patients will increase and the second one decrease.
For ion therapy, which is a qualitatively different type of radiation (because in each traversed cellular nucleus a carbon ion leaves 20 times more energy than a proton having the same range) further clinical studies are needed. It is in fact necessary to confirm that on ‘radioresistant’ tumours ions are more effective than photons and protons and that it is clinically safe to reduce the number of treatment sessions (ipo-fractionation). From other points of view such an approach is certainly advantageous since it implies a reduction of the costs and of the psychological burden to the patient.
Starting from these figures—and taking into account that in a population of 10 million and in a year about 20,000 patients are irradiated with photons—the number of hadron therapy treatment rooms needed within five/ten years are shown in the table. Two simplifying hypotheses have been made on the basis of clinical experience: (1) the number of sessions per patients scales as 1:2:3 for ions, protons and photons, respectively and (2) a photon (hadron) session lasts 15 min (20 min).
Pts. perRooms peryear inAverage No.Sessions perPts per yearRooms per10 millionRadiation107of sessionsday (12 h)(230 d)10 millionpeopletreatmentpeopleper patientin one roomin one roompeopleFactor ≈Photons20304837054 82103Protons 2.420364105.88(12%)103C ions 0.610368300.71(3%)103
The estimated numbers of rooms come out to be in the easy to remember “rule of thumb” 1:8:82.
Since a typical hadron therapy centre has 3-4 rooms, the figures of the table say that a proton (carbon ion) centre would be needed for about every 5 (40) million people. If the carbon centre is ‘dual’ and patients are treated also with protons, the number of inhabitants who can be served decreases from 40 to about 30 millions.
These arguments indicate that the development of hadron therapy requires a change with respect to the presently dominating ‘paradigm’, which sees a multi-floor building serving 5 million people (or many more in the carbon ion case) because it features one accelerator and 3-4 gantries. In the long term, a more flexible and patient-friendly paradigm will most probably dominate being based on a single-room accelerator/gantry system for either protons or light ions (carbon), which is constructed on a relatively small area (about 500 m2).
At present, small or large radiotherapy departments run 1-2 or 5-6 electron linacs respectively so that, on average, 8 conventional rooms are present in 3-4 hospitals covering a population of 1.5-2 millions. To maintain the proportions appearing in the last column of the table, two uses of such single-room facilities can be envisaged:                a single-room proton facility is “attached” to one of these hospitals but also serves 2-3 others;        a single-room carbon linac facility is “attached” to an already existing proton therapy centre which serves many million inhabitants but accelerates carbon, and        possibly other light ions, to an energy which is not sufficient to treat deep seated tumours.        
Proton accelerators which are mounted on a gantry rotating around an axis, and thus the patient, have been considered previously. In the 80's a rotating 60 MeV superconducting cyclotron for neutron therapy was constructed by H. Blosser and collaborators for built for the Harper Hospital (U.S. Pat. No. 4,641,104). Following this realization, more than fifteen years ago a 250 MeV superconducting cyclotron for proton therapy was proposed (H. Blosser et al, Medical accelerator projects at Michigan State University, Proc. 1989 Particle Acceleration Conference, IEEE, 1989, 742-746). Recently the construction project of a single room apparatus based on a rotating synchrocyclotron has been announced (http://web.mit.edu/newsoffice/2006/proton.html, press release of MIT, 28 Aug. 2006).